The best killer is the shot that is placed properly. So far, no one has mentioned trajectory. With a big, heavy bullet you are gaining nothing that will help you in a hunt. At ranges much beyond 100 yards the rainbow trajectory of your big heavy bullet means it will be almost falling down towards the target instead of at it. Unless you have precise knowledge of the range of the target and similarly precise knowledge of where that bullet is going at that exact distance you will overshoot or undershoot every time. I believe your imagination is carrying you into a realm that will make your dream hunting rifle a nitemare. I suggest you get your rifle in a .54 or .58 designed for patched round balls and enjoy.
Something nobody has mentioned yet was wind drift. Mountains are often rather breezy. A conical is far superior in this regard.
But the idea that a conical has much more of a rainbow trajectory isn’t exactly true. I ran the numbers (900’ elevation and 10 mph cross wind with 25 yd increments) for my .50 cal using 70 grns of 3F Olde E/Swiss/T7 and the 320 grn Lee REAL with a 0.189 BC and a 177 grn ball with a BC of 0.069. The first number is the trajectory and the second is wind drift:
The ball, zeroed at 100 yds, and starting around 1825 fps shows:
1.1”/0.3”, 2.0”/1.2”, 1.&”/2.8”, 0.0”/5.1”, -3.7”/8.0”
The conical starting out around 1450 fps shows:
1.3”/0.2”, 2.2”/0.5”, 1.8”/1.2”, 0.0”/2.1”, -3.3”/3.2”
That same conical with a zero at 125 yds shows:
2.0”, 3.6”, 3.8”, 2.7”, 0.0”, -4.3”
As we can all see the ball is actually coming down at more of an angle that the conical zeroed at 100 yds and striking at 125 yds. So the idea that the conical, on the same path, has more of a rainbow trajectory and is coming in at more of a downward angle.
We also see the conical won’t be pushed anywhere near as much as a ball, and, for me at least, wind speed is harder to estimate than range out to 100-150 yds.
We also see that the REAL, in this instance, can easily be used out to 150 yds whereas there’s no way I’d try that with a ball, especially on elk, and especially if it’s not a calm day. And what we see with the REAL sighted at 125 yds is that it’s quite good, especially on something large like elk, out to 150 yds using the point blank system, and peep sights might work rather nicely for this.
In regards to conicals I’d think a .45 or .50 would be plenty, but with a ball I wouldn’t want less than a .54.